This invention relates to a device for the precision grinding and polishing of surfaces of a workpiece which surfaces are situated in the plane of a reciprocating tool which serves as the carrier of the grinding or polishing medium. The invention is particularly useful for the processing of steel shapes or molds.
The removal of roughness or unevenness on workpieces caused by procedures such as turning, milling, or eroding, particularly on steel shapes or molds causes formidable difficulties and demands comparatively large amounts of manual labor. Usually the workpiece is clamped firmly for that purpose and is processed by the aid of a to and fro oscillating tool supplied with a grinding medium and guided by hand. It is important that the roughness of the workpieces are reduced to the extent that complete mold release results when the molds are used in connection with injection molding or diecasting.
An object of the present invention is to remove these defects which are of great importance in the preparation of molds and to create a device for precision grinding and polishing as described above, thereby producing a considerably improved result and a considerable saving of time.
The present invention solves this problem by the provision of a device which consists of a base to accept a workpiece movable in one plane and also consists of a stand rigidly connected to the base. The stand is provided with a carrying arm which is adjustable in the direction of all three space coordinates and which is furnished at its free end with an oscillating drive. The oscillating drive is connected to a polishing or grinding tool which serves as the carrier for the polishing or grinding medium.
The arrangement of the present invention differs from the heretofore well known arrangements insofar as the workpiece is no longer firmly clamped down but rather is arranged in such a way that it may be moved in one plane. On the other hand, the oscillating drive with the polishing and grinding tool is fastened to the stand and connected to a clamping arrangement in such a way that maximum adjustability of the stand makes it possible to clamp the workpiece in every possible position so that the workpiece may be practically acceptably treated on all surfaces of interest.
It has been found that it is remarkably easier and simpler to make the workpiece movable and to move it towards or to press it against the tool. A surprising advantage of the arrangement according to the present invention is that it obviates the heretofore needed frequent change of grain size of the grinding medium or grinding paste. It is now possible to use one paste of rather small grain size during the entire working period.
Finally it is particularly important that the device according to the present invention makes it possible to use on the device of the present invention the electrodes previously used for spark erosion on another machine as carriers of the grinding or polishing medium, thus as grinding or polishing tools, because the consecutive grinding or polishing does not offer any difficulties whatsoever. The economy or amount of time saved is more than 50 percent, for example, when a device according to the invention is used to precision grind a workpiece which was previously produced by spark erosion and then followed consecutively by the precision grinding on the device of the present invention. At the same time a considerable improvement of surface quality is obtained. The surface shows, when the device of the present invention is used, a uniformity and exactness impossible to obtain by manual work.
A further embodiment of the invention encompasses an accepting mechanism for the workpiece which consists of a carrying plate upon which the workpiece rests. The carrying plate is disposed upon a baseplate which is solidly connected to a stand and which carrying plate is movable in the direction of both coordinates in the plane of the baseplate. The mobility of the carrier plate which accepts the workpiece is sufficiently large to lead the workpiece, which is solidly fastened to the carrier plate, towards the tool by manually moving the carrier plate. Preferably the carrier plate may be mounted on an axial ball bearing which is arranged on its bottomside and which is movable in its own plane. Preferably a cage containing a multiplicity of ball bearings is provided between the baseplace and the carrier plate.
In another alternative arrangement of an accepting mechanism for the workpiece, there may be provided a turntable which is arranged upon the baseplate which is connected to the stand and which is rotatable around an axis vertically disposed relative to the baseplate. In every case it is important to keep the workpiece mobile and, on the other hand, to lock the workpiece in position towards the tool by aid of the stand while the tool is kept oscillating by the oscillating drive.
The invention encompasses a stand perpendicular to the baseplate and provided with a stand bushing which can be adjusted as to height, which can be rotated, and which is lockable. On the stand bushing there is provided a support arm having a longitudinal axis extending transversely to the axis of the stand and arranged in such a way that it may be moved along its longitudinal length. Thus freedom of movement is provided in two directions, that is, a swivel movement in a horizontal plane and an adjustability as to height in a vertical plane between the stand and its bushing. The stand has one more freedom of movement by the capability of the support arm to be moved along its length.
It is particularly advantageous to arrange between the stand and the stand bushing a self-restraining rack and pinion drive so that the stand bushing may be adjusted as to its height upon the stand. According to another feature, the rack and pinion may consist of a rack which may be swingably guided in a longitudinal groove upon the surface of the stand bushing parallel to its axis. The rack meshes with a pinion gear attached to the stand bushing and the gear is connected to a handwheel. Practically, the stand bushing is capable of swinging 360.degree. so that the tool may be used also on workpieces extending beyond the supporting device, for example on exceedingly large workpieces.
In another feature of the present invention the carrier arm is disposed in a carrier bushing which is connected to the stand bushing, and this carrier bushing may, as the present invention furthermore provides, be pivotable around its own axis and also pivotable around an axis which is perpendicular to the axis of the stand bushing. This inclination of the tool obtained by the aforementioned pivotal mounting makes it possible to machine undercuts or also planes which are inclined to the direction of removing from a mold.
According to another feature of the present invention the carrier arm may not be turned around in the carrier bushing and may have at its free end a header carrying the oscillating drive. The header is pivotable around the longitudinal axis of the carrier arm and around another axis which is perpendicular to the longitudinal axis and which lies in the oscillating plane of the carrier bushing. This mounting arrangement makes the tool still more mobile, a fact which will facilitate the approach of the workpiece to the tool.
It is particularly advantageous to arrange between the header and the carrier arm a bearing block arrangement having a bearing plate for the oscillatable holding of the header and a bearing yoke between whose legs there is provided a mating oscillating plate which is fastened to the end of the carrier arm. A transversely disposed set screw extends through the legs of the bearing yoke and the oscillating plate which set screw also serves as the oscillating axis. Considering that under practical conditions the angle of inclination of a plane as regards the direction of the removal from a mold cannot have any arbitrary size, the pivoting of the header towards the bearing block arrangement, that is the pivoting around the longitudinal axis of the carrier arm, may be limited, for example to 15.degree. towards both sides from the vertical.
The invention is furthermore characterized by fastening the driving motor of the oscillating drive to a support on the header and by arranging upon the axle of the drive motor an eccentric cam. A push rod mates with the eccentric cam and carries the tool at its lower end. Preferably the push rod is provided with a gripping device to hold the tool. The tool may lie along the longitudinal axis of the push rod and thus also in the direction of the oscillation of the moving tool. It may also be arranged at an angle, preferably a right angle to the oscillation, for example in order to treat a surface of the workpiece which is vertical to the carrier plate of the mounting installation for the workpiece.
The aforementioned eccentric cam has a regulatable lift and consists of two bushings which are under axial spring pressure and which mesh excentrically so that they may be arrested in varying angles against each other. The exterior of the bushings carry a connecting rod which is connected to the push rod. The lift of the eccentric cam may be regulated for example in the range of 0 to 2 mm in small steps or steplessly in order to adapt the motion of the tool to the varying surfaces which have to be worked on.
According to the present invention the device may be furnished with graduated angle scales to show the pivoting angles between the stand and the stand bushing, between the carrier arm and the bearing block, and finally between the bearing block arrangement and the header. This construction renders possible an exact positioning of the workpiece in space in which case frequently the setting of each scale is an exact function of all the other scales.
The stand bushing and the carrier bushing each are provided with a longitudinal slot through which a setscrew poses transversely and which is tightened after each setting.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.